The purpose of this study is to determine the safety and efficacy of an experimental medication, midodrine, in treating patients who have symptoms of orthostatic hypotension. Orthostatic hypotension is a condition in which blood pressure falls when there is a change in body position from lying or sitting down to standing. Midodrine is a peripheral alpha-receptor agonist that acts on both the arterial and venous systems, but has no direct central nervous system or cardiac effects. Its main effect is to increase the tone of the smooth muscle of the arteries and veins, leading to an increase in peripheral vascular resistance and a rise in systolic blood pressure. The primary hypothesis of this study is that midodrine improves quality of life by enabling patients to pursue activities of daily living.